题目内容
已知sin(
-α)=
(0＜α＜
)，则cosα=______．
| π |
| 4 |
| ||
| 10 |
| π |
| 2 |
∵0＜α＜
，∴-
＜
-α＜
∵sin(
-α)=
，∴cos(
-α)=
∴cosα=cos[
-（
-α）]=cos
cos（
-α）+sin
sin（
-α）=
×
+
×
=
故答案为：
| π |
| 2 |
| π |
| 4 |
| π |
| 4 |
| π |
| 4 |
∵sin(
| π |
| 4 |
| ||
| 10 |
| π |
| 4 |
7
| ||
| 10 |
∴cosα=cos[
| π |
| 4 |
| π |
| 4 |
| π |
| 4 |
| π |
| 4 |
| π |
| 4 |
| π |
| 4 |
| ||
| 2 |
7
| ||
| 10 |
| ||
| 2 |
| ||
| 10 |
| 4 |
| 5 |
故答案为：
| 4 |
| 5 |
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